1. Field of the Invention
The present invention relates to an optical waveguide for a touch panel and a touch panel using the same.
2. Description of the Related Art
A touch panel is an input device for operating an apparatus by directly touching a display screen of a liquid crystal display device or the like with a finger, a purpose-built stylus or the like. The touch panel includes a display which displays operation details and the like, and a detection means which detects the position (coordinates) of a portion of the display screen of the display touched with the finger or the like. Information indicating the touch position detected by the detection means is sent in the form of a signal to the apparatus, which in turn performs an operation and the like displayed on the touch position. Examples of the apparatus employing such a touch panel include ATMs in banking facilities, ticket vending machines in stations, portable game machines, and the like.
A detection means employing an optical waveguide is proposed as the detection means for detecting the portion touched with the finger and the like on the above-mentioned touch panel (see, for example, US Patent Application Laid-Open No. 2004/0201579A1).
Specifically, the touch panel includes optical waveguides provided around a periphery of a display screen of a rectangular display. The touch panel is configured such that a multiplicity of light beams parallel to the display screen of the display are emitted from a light-emitting portion of a light-emitting optical waveguide provided on a first side portion of the display screen of the display toward a second side portion, and the emitted light beams enter a light-receiving portion of a light-receiving optical waveguide provided on a second side portion. These optical waveguides cause the emitted light beams to travel in a lattice form on the display screen of the display. When a portion of the display screen of the display is touched with a finger in this state, the finger blocks some of the emitted light beams. Thus, the light-receiving optical waveguide senses a light blocked portion, whereby the position of the above-mentioned portion touched with the finger is detected.
On the other hand, the light beams emitted from an optical waveguide directly into the air diverge radially. In this state, optical transmission efficiency is low, and it is impossible to accurately detect the above-mentioned position of the portion touched with the finger. To solve the problem, an optical transmission device has been proposed in which the optical transmission efficiency is enhanced (see, for example, Japanese Patent Application Laid-Open No. 2003-4960). This conventional optical transmission device is schematically shown in FIGS. 7A and 7B. This optical transmission device includes an optical waveguide 100 and a lens device 20. The above-mentioned lens device 20 includes a mounting surface portion 21 for placing the optical waveguide 100 thereon, and a thick strip-shaped lens 22 formed to protrude from a front edge portion of this mounting surface portion 21. This strip-shaped lens 22 has a lens surface (a right-hand surface shown) of an arcuate configuration as seen in sectional side view so as to bulge outwardly (with reference to FIG. 7B). The above-mentioned optical waveguide 100 includes an under cladding layer 12, cores 13, and an over cladding layer 14 which are stacked in the order named. Each of the above-mentioned cores 13 has a front end portion formed as a lens portion 130 of a semicircular configuration as seen in plan view and exposed to the outside. This lens portion 130 has a lens surface (a front end surface) of an arcuate configuration as seen in plan view so as to bulge outwardly (with reference to FIG. 7A). In such an optical transmission device, when light beams S emitted from each of the cores 13 pass through the lens portion 130 provided in the front end portion of each of the cores 13, the light beams S are restrained from diverging in a direction parallel to the mounting surface of the above-mentioned mounting surface portion 21 (a horizontal direction) by refraction through the lens portion 130 of the semicircular configuration as seen in plan view. Thereafter, when the light beams S pass through the strip-shaped lens 22 of the above-mentioned lens device 20, the light beams S are restrained from diverging in a direction orthogonal to the above-mentioned mounting surface portion 21 (a vertical direction) by refraction through the strip-shaped lens 22 of the arcuate configuration as seen in sectional side view. The use of such an optical transmission device with enhanced optical transmission efficiency as an optical waveguide device for a touch panel enables the touch panel to accurately detect the position of the portion touched with the finger.
In the above-mentioned conventional optical transmission device, however, it is necessary to bond the optical waveguide 100 and the lens device 20 to each other, with accurate alignment achieved between the lens portion 130 provided in the front end portion of each of the cores 13 of the optical waveguide 100 and the strip-shaped lens 22 of the lens device 20. Unless the alignment is performed accurately, the divergence of the light beams S is not appropriately restrained on the light-emitting side, and, consequently, the position of the portion of the display screen of the display touched with the finger cannot be detected accurately. However, the accurate alignment requires precision and is hence difficult. It is labor- and time-consuming to achieve the accurate alignment.